Modified magnetic momentum slit including a pair of c-type magnets



Nov. 28, 1967 B E H E AL 3,355,586

MODIFIED MAGNETIC MOMENTUM SLIT INCLUDING A PAIR OF C-TYPE MAGNETS Filed Dec.r25, 1964 3 Sheets-Sheet 1 52 62 56 I INVENTORS 64 BENGT HED/N BY HAB/B BRECHNA ATTORNEY Nov. 28, 1967 Filed Dec. 25, 1964 H. BRECHNA ETAL MODIFIED MAGNETIC MOMENTUM SLIT INCLUDING A PAIR OF C-TYPE MAGNETS Sheets-Sheet 3 0 gap 2 crh. gap

Center 0 0.2" \centerl 7 7 W Va TURNS 20 TURNS 9.= 775 0. PER. POLE 20o mag; P. PER POLE 200 A 4 cmv gap 0 2" \\center 2O TURNS INVENTORS 200 0. m. PER. POLE BENGT HED/N BY HABIB BRECHNA /Kr- 1 A ATTORNEY United States Patent 3,355,586 MODEFEED MAGNETIC MOMENTUM SLIT IN- CLUDING A PAIR OF C-TYPE MAGNETS Habib Brechna, Palo Alto, Calif., and Bengt Hedin, Geneva, Switzerland, assignors to the United States of America as represented by the United States Atomic Energy (Zomrnission Filed Dec. 23, 1964, Ser. No. 420,835 6 Claims. (Cl. 250-413) ABSTRACT OF THE DISCLOSURE A pair of C-type magnets that each develop a sharply defined magnetic field between respective poles across a main gap along opposite sides of a magnetically neutral slit. Each pole includes a coil, a central core, and an outer piece that encloses the coil and functions as a slit side. The outer piece is magnetically connected with the central core at the outer end of the coil. There is a small gap, substantially smaller than the main gap, between the central core and the outer piece across the face of each pole. Charged particles centrally directed through the slit are not affected by the magnetic fields. Particles that are not cent-rally directed enter one of the magnetic fields to be forced along a curved path for momentum analysis or controlled dumping.

The present invention relates generally to a device for separating charged particles of a given momentum range within high energy beams, and in particular to a particle beam deflecting slit for separating and guiding particular desired portions of a charged particle beam in predetermined directions.

Conventional systems for deflecting or splitting multienergy atomic particle beams, e.g., in linear or other accelerators, have used solid masses of common materials such as copper or lead, disposed to define a slit through which the beam is directed, wherein the dimensions of the slit are determined mainly by the average momentum of the particles in the beam. In this type of beam slit a part of the beam is absorbed by the solid mass while the remaining, desired portion of the beam is allowed to pass through the slit. There results a serious cooling problem due to the heat generated from beam absorption by the solid mass of the slit, especially in the case where an extremely high energy beam is being handled. To avoid the problem of heat dissipation caused by the beam striking the slit, beam separators utilizing two C-type bending magnets have been designed, which impart the desired divergence and thus separation of the beam. In order to compensate for neutralized stray fields in such C-type bending magnet separators, current carrying metal sheets are placed over the pole tips of the magnets. Utilization of such a configuration, although of operative design, tends to give incomplete cancellation of the unwanted portion of the beam. In addition, the electric insulation utilized therein is generally exposed to the damaging effects of the beam, and the construction thereof is therefore undesirable and subject to unsatisfactory operation.

The present invention provides a uniquely designed magnetic momentum slit wherein the particular shape, configuration, and disposition of current-carrying conductors mounted within the slit structure provides a more complete cancellation of the generated magnetic fields which cause, in turn, a more precise separation of beams or beam portions without giving rise to problems of beam incidence upon the apparatus and the resulting heat dissipation problems associated therewith.

Accordingly, it is an object of the present invention to provide a beam deflecting device for separating atomic particle beams to form individual beams of particles of predetermined energy ranges having desired angles of deflection.

It is another object of the present invention to provide a magnetic momentum segregating slit which utilizes a particular magnetic field configuration to separate beams through desired angles of deflection.

Still another object of the present invention is to provide a magnetic momentum slit in which the magnetic field generating windings and associated insulation is protected from the damaging effects of beam radiation.

It is yet another object of the present invention to provide a magnetic momentum slit of unique construction wherein the width of the cancelled magnetic field region generated by the slit is adjustable, whereby the width of the undeflected beam passing therethrough may be varied.

It is still another object of the present invention to provide a magnetic momentum beam slit capable of deflecting charged particle beams into further diverging beams without scattering the particles therein, to thus maintain the optical qualities of a desired portion of the beam.

Still another object of the present invention is to provide a magnetic beam slit which is especially constructed to avoid interrupting desired portions of a charged particle beam, to make possible the controlled dumping of the undesired portions of a beam over a large area.

Other objects and advantages will be apparent in the following description and claims considered together with the accompanying drawing, in which:

FIGURE 1 is a partially sectioned, perspective view of a simplified magnetic momentum slit of the present invention utilizing two magnets in facing opposed configuration;

FIGURE 2 is a cross-section view of the magnetic momentum segregating slit of FIGURE 1 showing the magnet construction in greater detail;

FIGURE 3 is a cross-section view exemplifying an alternative construction of the slit of FIGURE 2;

FIGURE 4 is an enlarged, partially sectioned View of the slit of the invention showing various related dimensions thereof;

FIGURES 5, 6 and 7 are graphs of the magnetic field generated by apparatus of the invention constructed with successively larger slits of 0 cm., 2 cm., and 4 cm., respectively, wherein the field values of each graph are taken along the central plane, and along planes located 0.2 inch and 0.3 inch above the central plane.

The present invention comprises basically, two C-type magnets having slots formed into, and along, the inner facing pole surfaces thereof. The slots are particularly situated and of a preselected cross section to provide the desired unique field configuration. Current carrying vw'ndings are disposed in the slots and are designed and wound to generate a magnetic field which exhibits a sharp transition in field strength in the central region of the magnet between the pole surfaces due to the cancelling effects of the slit configuration. The generation of such a sharp transition in field strength by means of the coil and slot configuration provides a magnetic slit with more sharply defined beam deflecting regions, and thus a more positive and eificient separation of charged particle beams. Furthermore, unlike conventional slits, the undeflected central beam delivered by the present invention makes no contact with any metallic portions of the apparatus and is thus undisturbed. The outer deflected beams can be directed to a desired experimental station, or to a dumping region, likewise without contact with any portion of the slit apparatus.

Referring to FIGURE 1 there is shown a magnetic momentum slit 10 which illustrates the unique construction and associated operation of the present invention. Briefly,

the momentum slit 18 comprises a first and second C-type magnet 12 and 14 respectively, assembled in facing opposed relation to define centrally therethrough an elongated aperture or gap 16 of generally rectangular crosssection. The magnets 12 and 14 are spaced apart a preselected distanoe, herein termed the slit width, commensurate with the desired width of the undeflected central portion of the beam being transported therethrough as discussed further, infra. Each of the magnets 12, 14 are formed of a vertical yoke 18, 20 respectively, and two horizontal yokes 22, 24 respectively. Gap 16 therefore, is bounded, and thus defined by pairs of pole tips 26, 28 of magnets 12, 14 respectively. Magnet 12 has two pairs of axially extending slots 30, 32 formed in the facing pole tips. Coils 34 and 36 are disposed in the pairs of slots 30, 32 respectively, in imbedded relation to the surfaces of the pole tips 26 of the magnet 12. Magnet 14 likewise has two pairs of axially extending slots 38 and 40, wherein respective coils 42 and 44 are similarly embedded.

Referring now to FIGURE 2, there is shown one embodiment of the magnetic momentum slit 10 exemplifying in greater detail a construction thereof, employing the concept of the present invention. More particularly, the two C-type magnets 12, 14 are formed of vertical yokes 46, 48 respectively, which are in turn secured in integral relation to horizontal yokes 50, 52 and 54, 56 respectively by means of a plurality of spaced, threaded bores in the yokes through which are secured bolts 58. The C-type magnets 12, 14 are assembled as a unit with a predetermined slit spacing therebetween by means of imbedded mounting bars 60, 62 extending the length of the magnets and secured thereto by means of threaded bores in the yokes and matching, threaded bolts 64. Yokes 50, 52, 54 and 56 terminate in facing, opposed pole tips 66, 68, 70 and 72 respectively to form therebetween the aperture or gap 16. Coil enclosing shims 74 are secured, as by means of set screws, to the ends of horizontal yokes 50, 52, and similar coil-enclosing shims 76 are secured to the horizontal yokes 54, 56. Referring particularly to magnet 12, the horizontal yokes 50, 52 are machined along the lateral portions thereof, to form stair-stepped slots wherein are disposed coils 78, 80 of matching cross-sections. Coils 78, 80 are formed of a plurality of separate windings 81 wherein the cross-section of each winding matches the cross-section of the portion of the slot in which it is disposed and which is defined between the yokes 50, 52, and the yoke 46 and shims 74 upon assembly of the magnet 12. The windings, in turn, are formed of multiple turns of copper bar 83, preferably of square cross-section. Coils 78, 80 could be formed of a single coil having a crosssection conforming to the entire stair-stepped slot crosssection. However, for simplicity of construction and ease of assembly the use of a plurality of windings stacked together is much preferred. Likewise, the slots, as well as the coils 78, 80 need not be stair-stepped but could in fact have a trapezoidal or smoothly tapered, cross-section. However, such a smoothly tapered, cross-section construction would be more difficult to construct and assemble than the stair-stepped cross-section herein employed.

As shown in FIGURE 2, magnet 14 is constructed with a configuration identical with that of magnet 12, wherein coils 82', 84 are disposed within stair-stepped or staggered slots of matching cross-section. The coils 82, 84 are secured about the machined portions of the yokes 54, 56 respectively by the clamping action of the vertical yoke 48 and shims 76, upon assembly of the magnet 14.

As may be seen in FIGURES 1 and 2, the slots formed in yokes 50, 52 and the tips of shims 74 are machined to provide upon assembly of the magnetic momentum slit 10, slot openings 86, 88 respectively therein which extend along the length of the pole tips 66, 68 in register with the adjacent windings of coils 78, 80. Likewise yokes 54, 56 and shims 76 are designed to provide, upon assembly thereof, slot openings 90-, 92, which extend the length of the pole tips 70, 72 in register with the respective adjacent winding of coils 82, 84. The transition in the generated field strength is in part dependent upon the dimensions of" the slot openings 86, 88, 90, 92 relative to the slit width between magnets 12, 14 and the gap width between the facing pole tips 66, 68 and 70, 72, as is further described infra. Application of current to the coils 78, 80, 82, 84 generates 'a magnetic field having a configuration essentially as shown by field lines 94. Accordingly, as depicted in FIGURE 2 there exists a field-free region along the axis of the magnetic momentum slit 10 between the adjacent tips of the shims 74, 76.

Referring now to FIGURE 3, there is shown an alternate embodiment of the present invention utilizing essentially the coil and shim configuration shown in FIGURE 2, wherein however, the yoke structure is changed. In such an embodiment, the vertical yokes 46, 48 are of the same general construction as those of FIGURE 2. However, the horizontal yoke-pole tip combination of FIGURE 2 is replaced by single yokes 98, 180 which extend between the vertical yokes 46, 48 and are secured thereto by means of threaded bores and bolts 102. Pole pieces 104, 106 are secured as by means of bolts 108 to the horizontal yokes 93, respectively. Coil enclosing shims 110 are likewise secured to the horizontal yokes 98, 100 by forming flanges along the length thereof and bolting same against the horizontal yokes by means of bolts 112, to thus form onehalf of the momentum slit 10. The opposite half of the slit 10 has a configuration identical to the half hereinbefore described, and comprises. pole pieces 114 and 116, which are secured to horizontal yokes 98, 100 respectively. Coil enclosing shims 118 are disposed against the pole pieces 114, 116 and secured in position by the flanged edge and the bolts 112.

Referring now to FIGURE 4, there is shown in greater detail various dimensional relationships as taught by the invention, whereby optimum field configurations, viz, field cancellation, and thus magnet efficiency, is achieved. As heretofore mentioned, it is desirable that the centrally extending portion of the gap 16, herein termed region A, be free of any magnetic field. Accordingly, within region A the magnetic field is defined by the following relationships.

E is the magnetic field taken along the x axis. B is the magnetic field taken along the y axis. k and k are constants.

B is the magnetic field well inside the gap.

B A is the magnetic field within region A.

To obtain the desirable magnetic field configuration within region A, B and B should be made linear, and k and k should be made as small as possible.

To arrive at such a situation, it is desirable within a region B of slit 10 to shape the pole contours and coil configurations according to the potential function wherein x is the distance along the x axis. y is the distance along the y axis. B is the magnetic field well inside the gap.

r is equal to one-half the aperture width. a is one-half the slit width between slots.

Additionally, with regards to a region C of the magnet construction, it is desirable that the generated magnetic field be homogeneous. Therefore B is constant in region C, with where l is a constant, and is very much less than 1. For good optical conditions, I, should have a value within the range of from 10- to 10- If the magnets are constructed utilizing the above conditions and relationships, the resulting magnetic field generated by the momentum slit 10 is defined by curve 96. The field is, in essence, equal to zero through region A, rapidly increases linearly to a specific value through region B and is held constant at the field value through region C.

The resulting field configurations generated by the magnetic momentum slit for various slit widths are shown in FIGURES 5, 6, and 7. The values of the respective fields are taken along a central plane passing through the mag netic slit, and along planes passing 0.2 and 0.3 inch above the central plane respectively. FIGURE 5 shows a slight variance of field within the region A, thereby denoting the existence of a slight field Within such region. However FIGURES 6 and 7, wherein the slit width is made equal to 2 centimeters and 4 centimeters respectively, there may be seen to exist essentially a field-free region within the region A. Additionally, it is to be noted that the transition from the field-free region to the generated magnetic field is extremely sharp.

While the invention has been disclosed with respect to several embodiments, it will be apparent to those skilled in the art that numerous variations and modifications may be made within the spirit and scope of the invention and thus it is not intended to limit the invention except as defined in the following claims.

What is claimed is:

1. A magnetic momentum analyzing slit for selectively segregating particles of a desired momentum range from a particle beam comprising;

(a) magnetic field generating means disposed in the path of said beam including a pair of C-type magnets having magnetic poles of substantially rectangular cross-section, said magnet poles defining pairs of facing pole tips having substantially parallel opposing surfaces, said magnets being spaced in circumjacent relation about a centrally extending axis and aligned to form a main gap having boundaries lying in opposing parallel planes defined by the opposing surfaces of said pole tips, said magnets being spaced apart to form a slit opening therebetween intersecting said main gap;

(b) said pole tips having pairs of slots formed along their length and recessed within the surfaces thereof, and forming slot openings between said surfaces and slots, wherein the slot openings are of relatively smaller cross-section than the cross-section of the slots;

1 percent (c) annular coils disposed within each pair of slots and substantially in register beneath said slot openings, said coils lying in a plane parallel with the surfaces of said pole tips;

((1) and current source means for energizing said annular coils.

2. The magnetic momentum analyzing slit in accordance with claim 1 wherein said slots formed in said pole tips have a cross-secti0n of increasingly greater width approaching said slot openings, and said coils have a cross-section matching and filling the cross-section of said slots.

3. The magnetic momentum slit in accordance with claim 2 wherein said pair of C-type magnets are disposed apart a preselected variable distance in facing opposed spatial relation to define a slit opening of variable width, the intersection of the main gap thereof and said variable slit opening forming an elongated generally rectangular beam aperture of variable width therealong.

4. The magnetic momentum slit in accordance with claim 1 wherein said slot configuration further comprises a first slot recessed into each of said pole pieces along the lengths thereof near the edge thereof nearest said slit opening, a second slot parallel to the first slot and formed within said pole tip a substantial distance from said first slot, wherein the volume of said slots communicates with said main gap via the slot openings extending therealong, and the potential function of said main gap between the facing pole tips is substantially shown by the relationship:

wherein B is the magnetic field well inside the gap,

x is any perpendicular distance from said central axis along a central palne within said main gap,

3 is any perpendicular distance from said central axis along a central plane within said .slit opening,

r is equal to one-half the distance between said boundaries of said main gap,

a is equal to one-half the distance across said slit opening.

5. The magnetic momentum slit in accordance with claim 4 wherein the cross-section of said slots defines a stair-stepped configuration of increasingly greater width approaching the pole tip surfaces, and said annular coils are formed of a plurality of stacked coil windings of assembled cross-section which matches the stair-stepped slot cross-section.

6. The magnetic momentum slit in accordance with claim 1, wherein each of said .slot openings has a width that is less than the distance between said boundaries of said main gap.

References Cited UNITED STATES PATENTS 3,201,585 8/1965 Ballam et al. 250-41.9

RALPH G. NILSON, Primary Examiner. A. L. BIRCH, Assistant Examiner. 

1. A MAGNETIC MOMENTUM ANALYZING SLIT FOR SELECTIVELY SEGREGATING PARTICLES OF A DESIRED MOMENTUM RANGE FROM A PARTICLE BEAM COMPRISING; (A) MAGNETIC FIELD GENERATING MEANS DISPOSED IN THE PATH OF SAID BEAM INCLUDING A PAIR OF C-TYPE MAGNETS HAVING MAGNETIC POLES OF SUBSTANTIALLY RECTANGULAR CROSS-SECTION, SAID MAGNET POLES DEFINING PAIRS OF FACING POLE TIPS HAVING SUBSTANTIALLY PARALLEL OPPOSING SURFACES, SAID MAGNETS BEING SPACED IN CIRCUMJACENT RELATION ABOUT A CENTRALLY EXTENDING AXIS AND ALIGNED TO FORM A MAIN GAP HAVING BOUNDARIES LYING IN OPPOSING PARALLEL PLANES DEFINED BY THE OPPOSING SURFACES OF SAID POLE TIPS, SAID MAGNETS BEING SPACED APART TO FORM A SLIT OPENING THEREBETWEEN INTERSECTING SAID MAIN GAP; (B) SAID POLE TIPS HAVING PAIRS OF SLOTS FORMED ALONG THEIR LENGTH AND RECESSED WITHIN THE SURFACES THEREOF, AND FORMING SLOT OPENINGS BETWEEN SAID SURFACES AND SLOTS, WHEREIN THE SLOT OPENINGS ARE OF RELATIVELY SMALLER CROSS-SECTION THAN THE CROSS-SECTION OF THE SLOTS; 